1. Field of the Invention
The present invention relates generally to chip-on-board optical packaging, and in particular, to an optical lid for use as a protective package and transparent lid for an image sensor provided on a board.
2. Background Art
Chip-on-board optical packaging is well-known in the art, and involves directly attaching an integrated circuit (which can be an image sensor) to a board, instead of providing the integrated circuit in the form of an encapsulated chip that needs to be soldered to the board. As a result, the bond wires that are used to bond the integrated circuit to the board are exposed and must be protected from damage. There are two known packaging approaches to protecting the image sensor integrated circuit in a chip-on-board environment.
The first approach provides a two-piece package, where a molded plastic ring is attached to the board surrounding the image sensor, and a clear plastic or glass lid is then attached to the ring. The ring and lid therefore takes the form of a hat with a clear top which functions as a package to protect the image sensor and its bond wires from damage. However, this approach suffers from several drawbacks. First, the existence of two joints, one between the ring and the board, and the other between the ring and the lid, makes it difficult to manufacture the entire assembly of the board, ring and lid. Second, the delicate manner of the assembly of the two pieces (ring and lid) increases the cost of production.
According to the second approach, the molded plastic ring is first attached to the board surrounding the image sensor, and a transparent molding compound, such as a clear epoxy, is then poured into the ring to encapsulate the image sensor. This approach also suffers from some drawbacks. First, there is the possibility of generating bubbles in the molding compound. Second, it is also difficult to keep the outer surface of the molding compound flat to ensure co-planarity with the lens of the image sensor, since distortions may form on the outer surface. Third, the materials for the molding compound are easily scratched. All of these problems would impair the optical performance of the image sensor.